From ad5d696ce6eb72c52ff99137c3476ea0447d9f5a Mon Sep 17 00:00:00 2001
From: AJ ONeal <aj@therootcompany.com>
Date: Mon, 20 Apr 2026 09:50:48 -0600
Subject: [PATCH] refactor: dataset.Add returns View[T] instead of Dataset[T]
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Group-managed datasets must never have Init/Sync/Run called on them.
Rather than patching with NopSyncer, introduce View[T] — a thin wrapper
that exposes only Load(). The compiler now prevents misuse: callers can
read values but cannot drive fetch/reload cycles directly.

Dataset[T] no longer needs a syncer when owned by a Group; View.reload()
delegates to the inner Dataset.reload() for Group.reloadAll().
---
 net/dataset/dataset.go                 | 23 +++++++++++++++++------
 net/ipcohort/cmd/check-ip/blacklist.go |  6 +++---
 net/ipcohort/cmd/check-ip/main.go      |  6 +++---
 3 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/net/dataset/dataset.go b/net/dataset/dataset.go
index c14d10a..99dc9e3 100644
--- a/net/dataset/dataset.go
+++ b/net/dataset/dataset.go
@@ -124,13 +124,24 @@ func NewGroup(syncer httpcache.Syncer) *Group {
 	return &Group{syncer: syncer}
 }
 
-// Add registers a new dataset in g and returns it. Fetch and reload are driven
-// by the Group — call Init/Run/Sync on g, not on the returned Dataset.
+// View is the read-only handle returned by Add. It exposes only Load —
+// fetch and reload are driven by the owning Group.
+type View[T any] struct {
+	d *Dataset[T]
+}
+
+// Load returns the current value. Returns nil before the Group is initialised.
+func (v *View[T]) Load() *T { return v.d.ptr.Load() }
+
+func (v *View[T]) reload() error { return v.d.reload() }
+
+// Add registers a new dataset in g and returns a View. Call Load to read the
+// current value. Drive updates by calling Init/Sync/Run on the Group.
 // load is a closure capturing whatever paths or config it needs.
-func Add[T any](g *Group, load func() (*T, error)) *Dataset[T] {
-	d := &Dataset[T]{syncer: httpcache.NopSyncer{}, load: load}
-	g.members = append(g.members, d)
-	return d
+func Add[T any](g *Group, load func() (*T, error)) *View[T] {
+	v := &View[T]{d: &Dataset[T]{load: load}}
+	g.members = append(g.members, v)
+	return v
 }
 
 // Init fetches once then reloads all registered datasets.
diff --git a/net/ipcohort/cmd/check-ip/blacklist.go b/net/ipcohort/cmd/check-ip/blacklist.go
index 3c47be4..6ab0ed6 100644
--- a/net/ipcohort/cmd/check-ip/blacklist.go
+++ b/net/ipcohort/cmd/check-ip/blacklist.go
@@ -82,9 +82,9 @@ func (s *Sources) Fetch() (bool, error) {
 // outbound may be nil if no paths were configured.
 func (s *Sources) Datasets() (
 	g *dataset.Group,
-	whitelist *dataset.Dataset[ipcohort.Cohort],
-	inbound *dataset.Dataset[ipcohort.Cohort],
-	outbound *dataset.Dataset[ipcohort.Cohort],
+	whitelist *dataset.View[ipcohort.Cohort],
+	inbound *dataset.View[ipcohort.Cohort],
+	outbound *dataset.View[ipcohort.Cohort],
 ) {
 	g = dataset.NewGroup(s)
 	if len(s.whitelistPaths) > 0 {
diff --git a/net/ipcohort/cmd/check-ip/main.go b/net/ipcohort/cmd/check-ip/main.go
index eb24965..afb23ea 100644
--- a/net/ipcohort/cmd/check-ip/main.go
+++ b/net/ipcohort/cmd/check-ip/main.go
@@ -185,7 +185,7 @@ func newGeoIPDataset(d *geoip.Downloader, edition, path string) *dataset.Dataset
 }
 
 func containsInbound(ip string,
-	whitelist, inbound *dataset.Dataset[ipcohort.Cohort],
+	whitelist, inbound *dataset.View[ipcohort.Cohort],
 ) bool {
 	if whitelist != nil {
 		if wl := whitelist.Load(); wl != nil && wl.Contains(ip) {
@@ -200,7 +200,7 @@ func containsInbound(ip string,
 }
 
 func containsOutbound(ip string,
-	whitelist, outbound *dataset.Dataset[ipcohort.Cohort],
+	whitelist, outbound *dataset.View[ipcohort.Cohort],
 ) bool {
 	if whitelist != nil {
 		if wl := whitelist.Load(); wl != nil && wl.Contains(ip) {
@@ -256,7 +256,7 @@ func printGeoInfo(ipStr string, cityDS, asnDS *dataset.Dataset[geoip2.Reader]) {
 	}
 }
 
-func cohortSize(ds *dataset.Dataset[ipcohort.Cohort]) int {
+func cohortSize(ds *dataset.View[ipcohort.Cohort]) int {
 	if ds == nil {
 		return 0
 	}